Phased arrays of antenna elements are generally widely used to control the direction and angular gain dependence of a beam for a waveform to be transmitted or received. In general, the larger the extent of a phased array arrangement, the narrower the beam that can be formed thereby, and thus the better is its directional accuracy and gain in the main beam direction. Also, the minimal wavelength λmin of radiation which can be optimally received and/or transmitted by a phased array arrangement depends on the spacing d between the elements of the phased array arrangement as follows λmin=2d. Specifically, the smaller the spacing d between the plurality of receiving/transmitting elements of a phased array, the shorter the wavelengths λ (λ>λmin=2d) which may be received/transmitted by the phased array with optimal directional resolution while avoiding/reducing directional ambiguity.
One technique for processing signals from phased arrays is disclosed for example in U.S. Pat. No. 8,022,874 co-assigned to the assignee of the present application. In this publication a respective electromagnetic parameter and spatial disposition of an unknown number of signal sources in a surveillance space simultaneously bombarded by multiple signals are determined by receiving multiple signals at each of a plurality of widebeam, wideband antennas equally spaced apart in a linear array. Respective antenna signals are simultaneously sampled to generate a two-dimensional array of values. A two-dimensional Fourier transform is computed whose peaks satisfy one or more predetermined criteria, each peak being indicative of a signal source in the surveillance space, whereby the location of the peak in the Fourier transform indicates the frequency and the azimuth of the respective signal source and the amplitude of the peak indicates the amplitude of the signal source. When implemented using two mutually perpendicular unified linear arrays (2D-ULA) or 2D (planar) array of receiving antennas, an additional Fourier transform of the two-dimensional Fourier transform generates, for each identified emitter, independent azimuth and elevation angles.
Also, U.S. Pat. No. 7,369,833 discloses a receive system providing enhanced directivity in the form of a narrowed receive beam and a relatively small antenna with performance comparable to a much larger antenna at similar frequencies. Received signals are converted to digital values and stored in a manner which enables subsequent processing directed to improving the resolution of the received signals and to reduce the associated noise corresponding to the received data samples. The Signal-to-Noise ratio of the received data signals is improved as a result of processing techniques made possible by the configuration of the antenna and the digitally stored nature of the received data.
U.S. Pat. No. 5,565,873 provides an antenna for a base station comprising a plurality of antenna arrays each capable of forming a multiplicity of separate overlapping narrow beams in azimuth, the arrays being positioned such that the beams formed by the arrays provide a coverage in azimuth wider than each array. Means are provided for operating two or more non-collocated narrow beamwidth antenna arrays to form jointly a broad beamwidth antenna radiation pattern wherein the time averaged antenna pattern is substantially null free.